With progress of higher-performance vehicles made in recent years, there have been proposed various rotation angle detectors (hereinafter called “RAD”) for detecting the rotary angle of a steering wheel (hereinafter called “SWH”). An example of such RAD is disclosed, for example, in Japanese Patent Non-examined Publication No. 2002-206910.
A conventional art RAD will be described with reference to FIG. 5.
On the circumference of rotating member 1, there is formed spur gear portion 1A. Rotating member 1 has engagement portion 1B to engage the shaft of SWH (not shown) inserted in the center thereof. Insulative resin-made detecting member 2 has a substantially planar top face. Spur gear portion 2A provided on the circumference of detecting member 2 is in a meshing arrangement with spur gear portion 1A on rotating member 1. Detecting member 2 has a cylindrical columnar protrusion 2B formed in the center of its underside. Protrusion 2B has magnet 3 mounted at its end by performing such an operation as insert molding.
Circular columnar shaft portion 4, made of a metal, is fixed by insert molding or the like to the center, i.e., the rotation axis, of detecting member 2, as projected upward.
Axes of shaft portion 4 and magnet 3 are each arranged substantially in alignment with the axis of detecting member 2.
There are provided a plurality of wiring patterns (not shown) on both sides of wiring board 5 disposed substantially parallel to the underside of detecting member 2. Further, magnetic sensor element 6 is mounted on the face opposite to detecting member 2. Magnet 3 and magnetic sensor element 6 arranged opposite to each other constitute sensor means 7.
Further, there is provided wiring board 8 connected with wiring board 5 via lead wire 9. On wiring board 8, there is formed control device 10 constructed of electronic parts including a microcomputer. Control means 10 is connected to an electronic circuit (not shown) on the vehicle body by way of a connector (not shown).
Further, cylindrical supporting member 11, made of an insulative resin, is fixed on to the top face of wiring board 5. Cylindrical supporting member 11, while surrounding protrusion 2B, supports the underside of detecting member 2 for rotation. Upper cover 12, made of an insulative resin, has shaft support 12A protruded downward from its underside, shaft support 12A having a diameter slightly larger than the diameter of shaft portion 4 of detecting member 2. Shaft portion 4 of detecting member 2 is inserted into shaft support 12A to be supported thereby for rotation.
Rotating member 1, wiring board 5, wiring board 8, and the like are covered by insulative resin-made case 13, insulative resin-made side cover 14, and upper cover 12, so that these are kept in place to configure RAD.
As SWH is turned in the above described configuration, rotary member 1 is rotated accordingly. Following this rotation, detecting member 2 with its circumferential spur gear portion 2A in mesh with circumferential spur gear portion 1A of rotating member 1 also rotates taking, as the center of rotation, shaft portion 4, which is supported by shaft support 12A protruded from upper cover 12. As detecting member 2 rotates, the magnetic field around magnet 3 mounted on the center of detecting member 2 changes. Then, the change in the magnetic field is detected by magnetic sensor element 6, and a detection signal with a substantially triangular waveform is output to control means 10. Thus, it is arranged such that control means 10 detects the rotation angle of rotating member 1 on the basis of the number of waveforms and a voltage value of the detection signal from magnetic sensor element 6. An angle of rotation of SWH can thus be detected. However, when such conventional RAD is mounted on a vehicle, there are also placed other equipment or parts on top of RAD. Accordingly, the height from the top face of detecting member 2 up to the top face of upper cover 12 is limited and, hence, length L1 of shaft support 12A formed between the top face of upper cover 12 and the top face of detecting member 2 becomes short. As a result, shaft portion 4 supported within shaft support 12A tends to show play or looseness during rotation.
Such play or looseness causes undesirable rotational deflections to magnet 3 provided at the bottom end of detecting member 2. Thus, conventional RAD is confronted with a problem that errors are liable to be produced in a detected angle of rotation.
The present invention is addressed to such a problem in the conventional art, and it is an object of the invention to provide RAD with high detection accuracy.